Electromagnetic timing devices



July 17, 1962 N. c. PICKERING ELECTROMAGNETIC TIMING DEVICES 3 Sheets-Sheet 1 Filed May 4, 1959 INVENTOR. NORMAN C. PICKERING ATTORNEY July 17, 1962 N. c. PICKERING 3,

ELECTROMAGNETIC TIMING DEVICES Filed May 4, 1959 3 Sheets-Sheet 2 Zia.

INVENTOR. NORMAN C. PlCKER/NG ATTORNEY July 17, 1962 N. c. PICKERING 3,045,160

ELECTROMAGNETIC TIMING DEVICES Filed May 4, 1959 3 Sheets-Sheet 3 FI 5B -CONTACT CLOSURE 45 ON MAKE sms 15 ON BACK SIDE o .010 O.l25 0.25\ 0.5 TIME SECS PORTION OF CYCLE DURING WHICH DRIVE CAMS ARE ENGAGED IN VEN TOR.

F I Q, 6 NORMAN c. PICKER/NG ATTORNEY United States Patent O 3,045,160 ELECTROMAGNETIC TIMING DEVICES Norman C. Pickering, Sag Harbor, N.Y., assignor to Charles Denning Limited, Sag Harbor, N.Y., a corporation of New York Filed May 4, 1959, Ser. No. 810322 4 Claims. (Cl. 318-128) This invention relates to timing devices and more particularly to electromagnetically-driven timing devices utilizing mechanically resonant systems to govern the timing function.

Timing devices such as watches and clocks are commonly driven from either of two basic energy sources, mechanical or electrical. Mechanical sources, include, for example, Weights and springs which yield their energy bit by bit to keep a mechanically resonant system in motion. .Electrical sources include AG in which the frequency of the source controls the timing function, and DC. in which the timing function derives from a mechanically resonant system, the energy being imparted thereto by means of electromagnetic techniques. It is the latter type of timing device with which the present invention is concerned, particularly those which make use of battery power. Important aspects of timing mechanisms using the frequency or natural period of a mec'hanically-resonant system maintained in motion by magnetic impulses are precise control of the timing and magnitude of the driving impulses and the manner of coupling the resonant system to the output to display the time reading. Thus problems of both an electrical and mechanical nature must be overcome if efiiciency and accurate timing over a long life are to be-attained in electromagnetical-ly driven timing devices of this type.

Accordingly, it is one object of the present invention to provide an improved, electromagnetically-actuated timing device operated from a DC. source.

Another object of the invention is to provide a timing device capable of retaining accuracy of operation over an extended period of time from an inexpensive battery power source.

Another object of the invention is to provide an electromagnetically actuated timing device having improved electronic and mechanical systems.

In accordance with the present invention, there is provided a timing device having a mechanically resonant balance staff to which driving energy is imparted by magnetic impulses through the agency of a timing motor in which the armature moves with the balance staff. In one preferred arrangement a single transistor amplitier circuit, which energizes a drive coil, is connected in a grounded emitter configuration and is operated through an underdamped switching arrangement controlled by the balance staif.

In another arrangement, the drive coil is incorporated in a transformer, the windings of which are connected at one end to the output of an electronic amplifier, which can also take the form of a single transistor. The" other ends of the transformer windings are connected across a resistor, one end of which is connected to ground through an electrical switch operated by the balance staff and the other end of which is connected to a D0. battery source. When the switch is closed periodically, the secondary winding is grounded to change the bias on the transistor to initiate amplifying action, with the re sulting current flow through the primary winding developing magnetic impulses to drive the balance staff as well as the clockwork.

In order to drive the time display or read-out portion of the device, there are provided a pair of contoured cams which move or oscillate as a function of the halance stafi motion to index a counting wheel coupled to the gear train. In one preferred arrangement, the counting wheel includes, on one surface, axially extending pins which are engaged first by one cam and then the other to cause the wheel to be rotated. On the other surface there are formed a myriad of radial detent teeth releaseably engaged by detent finger so that the counting wheel will always be in position to be driven by the cams. Also, the cams and pins are so arranged that in the event of'occasional extreme amplitudes of cam motion, causing the cams to back up into the pins, the counting wheel will be moved in a reverse direction, thereby preventing damage to any part of the instrument.

Other features and objects of the present invention will be apparent to those skilled in the art by referring to the following specification describing one preferred embodiment of the invention and taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a view, partly diagrammatic in nature, of a timing device as viewed in a direction perpendicular to the balance staff thereof;

FIGURE 2. is a view in horizontal section taken generally on the line 2-2 of FIGURE 1, looking in the direction of the arrows;

FIGURE 3 is a schematic diagram illustrating electrical circuitry for the timing device of FIGURES l and 2;

FIGURE 4 is a schematic diagram illustrating modified circuitry for use in the timing device of FIGURES 1 and 2;

FIGURES 5A and 5B are fragmentary views in enlarged scale of portions of the drive mechanism utilized in the timing devices, and

FIGURE 6 is a graph illustrating switch action and drive action over a complete cycle of oscillation of the balance staif of the timing device.

Referring to the drawings, and first to FIGURES 1 and 2 in particular, there is disclosed a timing device. in the form of a clock 10 in which the read-out indicators, in this case hands 11a and 1112, are driven through a gear train 12 coupled by a cam drive system 13 to be controlled by the balance staif assembly indicated generally by the numeral 14. The balance stalf assembly 14 is journalled in suitable bearings 14a and 14b for oscillatory, resonant movement dependent on torsion spring means which can take the form, for example, of a helical hairspring 15 connected at its inner end to the balance stafi? assembly and at its outer end to the frame of the clock.

The balance staff assembly 14 carries an armature 16 which, in the illustrated arrangement, is separated from the balance wheel mass 17. The armature 16 oscillates Within the pole pieces 18a, 18b of :a stator 18 carrying winding means 19. The winding 19 is connected, by means of electrical circuits described more fully below, to a DC. energizing source which can take the form for example of conventional type D flashlight cells 20. Control of the energization of the windings 19 from the battery source 20 is effected by switch means 21 (FIGURE 1) which can take the form of :a moving contact 21a which oscillates with the balance staff assembly :and a fixed contact 21b in the form of a flexible blade supported by the frame of the clock and adapted to be engaged by the moving contact 21a during a predetermined pe-- riod of each oscillation of the balance staff assembly. This contact assembly can take the form of that disclosed in the applicants co-pending application Serial No. 674,- 830, filed July 29,1957.

Referring to FIGURE 3, the winding means 19 on the field structure 18 is connected in a switched transistoramplifier circuit including a transistor 24 having its base electrode 2 4a connected to the switch means 21 which is 3 grounded, at the time of contact, through a ground connection 21a. The emitter electrode 24b of the transistor 24 is also connected to ground, as is the negative terminal of the DC. or battery power source 20. The winding 19 is connected between the positive terminal of the power source 20 and the collector electrode 240 of the transistor 24. Also connected between the positive terminal of the power source 20 and the base electrode 24a is a bias resistor 22. In a representative circuit arrangement, a three volt power source and a transistor such as type 2N406 were used together with a winding of 3,000 turns of number 36 wire. The resistor 22 has a value of 22K ohms. In such circuit arrangement, utilizing a contact closure angle of approximately 45 degrees of balance staff rotation, as indicated in the timing graph of FIG- URE 6 (thus providing a contact-closed interval of approximately 0.0l second) the circuit operates so that the switch 21 is underdamped to afford fifteen to twenty volt peaks during contact interval. The graph of FIG- URE 6 will be described more fully at a later point. In addition, the circuit operates to limit the current flow through the switch to less than 50 microarnperes. The utilization of a grounded emitter in the transistor amplifier circuit results in a low voltage drop across the transistor which permits grounding the negative pole of the battery.

Referring now to FIGURE 4, in which like parts are identified by like, primed reference numerals, the winding 19 on the stator 18' is in the form of a transformer including a secondary winding 19a and a primary winding 1%, both wound on the stator 18'. Connected across corresponding ends of the primary and secondary windings 19a and 19b is a resistor 22'. The secondary winding 19a is connected to ground through the contacts 21'. The primary winding 1% is connected to ground through the battery 20', polarized with its negative electrode grounded. The other end of the secondary winding 19a is connected by means of a conductor 23 to the base electrode 24a of a transistor 24. The emitter electrode 24b of the transistor 24' is connected to the other end of the primary winding 19b, while the collector electrode 24b is connected to ground. In a preferred arrangement a transistor of the alloy junction germanium p-n-p type was used together with a battery source of three volts and a transformer in which 2,000 turns of No. 32 wire were used for the primary winding 1% and 2,000 turns of No. 42 wire for the secondary winding 19a. The resistor 22 had a value of approximately 2,000 ohms.

In operation, with the switch means 21 open, full positive battery voltage is applied through the primary winding 1% of the transformer to the emitter electrode 24b of the transistor 24'. At the same time the positive voltage is also applied through the resistor 22' and the secondary winding 19a to the base electrode 24a of the transistor. For the majority of transistors a current will flow in the circuit configuration of approximately microamperes or less. When the switch 21 closes momentarily as the balance staff oscillates, a voltage pulse is applied to the windings of the transformer as the voltage in the base electrode 24a drops to zero through the ground connection. Current also flows from ground through the resistor 22 which, in the above-described arrangement, will be on the order of approximately 1.5 milliamperes. The switch construction is such that the contacts 21 are closed for approximately 2 percent of the time required for one complete oscillation of the balance stafi so that the average current flowing through the resistor 22 will be about 30 microamperes.

With the switch 21 closed and the voltage on the base electrode 24a dropping to zero, current rises rapidly in the primary winding 1%, and since the windings 19a and 19b are connected in the proper polarities to do so, an increase in primary current causes the voltage on the base electrode to drop while the rapidly rising voltage change which occurs quickly brings the emitter current in the transistor to a point of saturation. This rise of current will take place in a series of rapid alternating-current oscillations. Since these oscillations occur at a frequency which is high compared to the repetition rate of the switching cycle, the net effect is to build up the emitter current rapidly. After the transient pulse is over (less than a milli-second after the switch is closed), the voltage on the base electrode 24a becomes stabilized at zero potential. The emitter current is then limited only by the inductive reactance of the winding 1% and typically reaches sixty-three percent of full value in about 10 milliseconds. When the switch 21 opens, increased voltage on the base electrode 24a will occur to cause the emitter current to drop, and again the regenerative effect causes a rapid cutoff of the emitter current. Conditions then stabilize at the potentials necessary for minimum battery drain during the open period of the switch.

The current through the switch 21 is reduced to about 2 percent of the current value which would obtain were the circuit to take the form simply of a series circuit including the battery, the switch, and a winding on the stator 13, that is to say, without the transistor and transformer circuit configurations described above. Also, peak voltage across the switch is reduced to about 5 percent of what it would he were the current in the coil or winding to be broken directly by the switch. The current pulse in the winding, which is critical in preserving the isochronous character of the timing device, is shortened and steepened, making more effective use of the inherently limited battery voltage. The operation of the circuit is such that variations in the transistor characteristics are equalized by the biasing conditions and the regenerative changes of the electrode potentials. At the same time, changes in effective pulse current with decay or change of battery voltage are minimized.

Referring now to FIGURES 1, 2, 5A, 5B and 6, as the electrical circuits described above operate to maintain the balance staff 13 in oscillation at a natural resonant frequency, a certain portion of the energy is utilized to drive the hands 11a and 11b of the clock, through the ear train 12. In accordance with the present invention this drive takes place through the agency of the drive cam assembly 13, preferably although not necessarily mounted on the balance staff assembly 14. The drive cam assembly works in conjunction with a counting wheel 25 which rotates on a shaft 25a coupled to the gear train 12. The counting wheel 25 includes a circular array of twenty-four axially extending pins or teeth 25b (best seen in FIG- URES 1, 5A and 5B). The opposite side of the counting wheel 25 includes a series of radially arranged detents 250 which are releaseably engaged, one at a time, by a detent spring 26. The detent spring and detents hold the counting wheel releaseably in predetermined angular positions which, due to the inwardly converging walls of the detents, causes the counting wheel to assume predetermined angular positions, ie the pins 25b assume a position to be driven by the cams. In a preferred arrangement forty-eight detents having ninety degree taper angles Were used so that two increments of detent motion correspond to the spacing between two successive axial pins 25b.

The axially extending pins 251) of the counting wheel are engaged by a pair of cams 27a and 27b carried on a hub 28. As illustrated in FIGURE 5A, the upper surfaces of the cams 27a and 27b constitute drive faces which are formed with a sinusoidal curvature, each having minimum slope at the extremities with respect to the direction of movement during oscillation of the balance staff.

The cams 27a and 271) are juxtaposed along the axis of oscillation and are also inclined in opposite directions. By means of this arrangement, in relation to the angular spacing of the pins of the counting wheel, the counting wheel is indexed in a forward direction as indicated by the arrow 29 once for each swing of the balance staff.

-As illustrated in FIGURE A with the balance staff swinging in a clockwise direction as indicated by the numeral 30, the tooth 25b of the counting wheel will be received between the lower end of the cam 27b and the lower end of the cam 27a to be engaged by the upper surface of the latter, which then drives the counting wheel forward for one step of rotation causing, in the process, the detent spring 26 to enter a new detent 25c. Swinging out of engagement with the tooth, the balance staff continues its swing and then returns to present the pin 25b, which has just been pushed forward by the cam 27a, to the upper surface of the cam 27b, which drives the counting wheel forward for another step. The cycle then repeats'for the next pin.

In each case, it will be observed that the sinusoidal contour of the cams enables the balance staff to smoothly accelerate the counting Wheel and gear train from standstill to the point of maximum velocity. Noise and shock are reduced. Referring to FIGURE 6, in which one complete cycle of oscillation of the'balance staff is illustrated graphically it will be observed that the balance staff swings through arcs of approximately 200 degrees on either side of center and that a complete cycle or oscillation occurs in approximately 0.5 seconds. Thus, the gear train is stepped forwardly one increment each quarter second. Moreover, the angular positions of the cams and their lengths are so arranged that the driving action occurs only at the points of maximum velocity, i.e. near the center position of the balance staff and only for a fraction of the total time. It will be observed also that the electrical circuit is pulsed to energize the winding 19 for a small fraction of the travel, which for one direction of oscillation is substantially coextensive with the duration of cam engagement. For the other direction of travel of the balance staff a similar interval of cam drive occurs, but without the circuit being closed. This portion of contact closure for the return stroke is, as described in the co-pending application Serial No. 674,830, filed July 29, 1957 now' abandoned, approximately degrees of are, but is without electrical coupling. In other words, the contacts engage briefly, but due to-the action of insulating surfaces electrical current does not pass. Consequently, the balance staff swings freely for the majority of its travel and moreover is mechanically loaded only at points of maximum velocity. Friction is reduced in the system by molding the drive pins or teeth of the counting wheel, as one unit, in plastic such as nylon. The cam assembly can similarly be made as single unit.

In certain situations the balance statf of a clock is accelerated to extreme amplitudes which carry the cams in a. backward direction into the pins of the counting wheel. In such circumstance the upper surfaces of the cams 27a and 27b, as viewed in FIGURE 5A, engage the teeth. The arrangement of these inclined surfaces is such that the counting wheel is backed up for a step or portion of a step. Any breaking, bending, or jamming cannot occur. ,Also, detenting action occurs at the cams so that slight eccentricities in the counting wheel have no effect on the basic accuracy of the timing device.

While the invention has been described above having reference to a preferred embodiment thereof, it will be understood that it can take various other forms and arrangements. Thus, for example, the driving action of the balance staff into the gear train 12 through the cam escapement 13 can be eliminated by providing a separate flux path and electromagnetic driving system, energized from the same winding, for the gear train. The invention should not, therefore, be regarded as limited except as defined in the following claims.

I claim:

1. An electromagnetically-driven timing device having a mechanically resonant member and electromagnetic means to drive the member including winding means adapted to be connected periodically to a source of electrical energy to generate a magnetic flux field, complementary magnetic means movable with the member and adapted to be driven by the magnetic flux, amplifier means including input and output circuits and adapted to be energized by said source and having said winding connected in its output circuit, electrical contact means connected to be operated by oscillation of said member to actuate the amplifier to energize the winding means, said winding means including a magnetic field structure, a transformer having primary and secondary windings wound on the structure, means to connect the secondary winding in series with said contacts and the input circuit of the amplifier, and means to connect the primary winding in the output circuit of the amplifier.

2. An electromagnetically-driven timing device as set forth in claim 1, including a resistor connected between corresponding ends of the primary and secondary windings.

3. In a timing device having a frame, an oscillatory, mechanically-resonant member supported by the frame, and electromagnetic means to drive the resonant member, the invention comprising an armature movablewith the member, a field structure complementary thereto and including primary and secondary transformer windings thereon, amplifier means including a transistor having base, emitter and collector connections, a source of DC. electrical power, means including the primary winding of the transformer to connect one terminal of the DC source to the emitter connection, means including a resister and the secondary winding to connect said one terminal of the DC. source to the base connection, means to connect the other terminal of the DC. source and the collector connection to ground, and switch means responsive to oscillation of said member to periodically connect the base connection to ground through the second ary winding.

4. A timing device as set forth in claim 3, said switch means including a pair of electrical contact elements, one of which is movable with the armature to close the contacts at least once for each oscillation of the member.

References Cited in the file of this patent UNITED STATES PATENTS 2,572,989 Contant et al. Oct. 30, 1951 2,712,758 Schaaf July 12, 1955 2,838,693 Van Horn June 10, 1958 2,843,742 Cluwen July 15, 1958 2,853,849 Beyner Sept. 30, 1958 2,877,399 Shaull Mar. 10, 1959 2,900,786 I-I'etzel Aug. 25, 1959 

